Source : Free On-Line Dictionary of Computing

retronym
     
         A term invented to distinguish a subclass of things
        from new members of the superclass, where the distinction was
        previously not necessary, since the old subclass had been all
        there was of the superclass.
     
        For example, the retronyms "{snail mail}" and "{paper mail}"
        were coined by those for who "mail" was likely to mean
        {electronic mail}.
     
        While the English language in general has a few retronyms
        ("whole milk", "snow skiing", "acoustic guitar"), hacker
        jargon is necessarily (at points capriciously) rich in
        retronyms, e.g. {plaintext}, {natural language}, {impact
        printer}, {eyeball search}, biological {virus}.
     
        [More examples?]
     
        (2001-02-25)